This invention relates to metal organic frameworks (MOFs) having zeolite-net-like topologies, their methods of design, their modes of synthesis, and their modes of use.
Synthetic solid-state materials play a critical role in our economy and everyday life. We are at a critical juncture where both improvement of existing materials and new approaches to the design of novel materials are required to address the many technological challenges that face us concerning the environment, biomedicine, pharmaceutical science, energy, space exploration, superconductors, microelectronics, photonics, supercomputers, super-catalysts, chiral separations and hydrogen storage for fuelling applications. (Ozin, 2000). In spite of great progress in the area of solid state materials that has afforded refined porous solids such as zeolites, (Davis, 2002), the basic synthetic approaches have remained unchanged for much of the twentieth century; discovery of new materials has largely been serendipitous, using standard methods (Stein, 1993).
Zeolites, purely inorganic microporous crystalline solids constructed from tetrahedral building units sharing corners, are an important class of solid-state materials and are of major economic significance owing to the homogeneously sized and shaped openings and voids (Davis M. E., 2004; Corma, A. and Davis, M. E., 2004). These confined spaces permit their conventional use par excellence as shape- and size-selective catalysts, ion exchangers and adsorbents. These properties are closely related to the framework's structural features such as the size of the pore openings and cavities. Difficulties in altering the zeolite i) structural features in order to enclose extra-large cavities beyond the 1 nm prison (Paillaud et al., 2004) and/or ii) composition to contain a periodic array of intra-framework organic functionality (Yamamoto, K., 1998; Jones, C. W. et al, 1998) have thus far restricted their application to small molecules. Rational construction of tetrahedrally connected porous materials, related in their topological properties to zeolites with extra-large cavities and periodic intra-framework organic functionality, is an ongoing synthetic challenge, and it is of exceptional scientific and technological interest, offering great potential for innovative applications pertaining to large molecules, nanotechnology, optics, sensor-technology, medicine, etc. (Davis, M. E., 1997).
Assembly of finite supramolecular polyhedra and periodic extended networks from molecular building blocks (MBBs) offers great potential for the rational design and synthesis of functional materials and nanostructures (Cheetham, A. K., et al., 1999; Yaghi, O. M., et al., 2003; Seo, J. S., et al., 2000; Desiraju, G. R., 2001). This approach has been explored and, to some extent, has proven to be successful in metal-ligand directed assembly (Moulton, B. and M. J. Zaworotko, 2001; Hoskins, B. F. and R. Robson, 1990; Stang, P. J. and S. R. Seidel, 2002; Takeda, N., et al., 1999; Kitagawa, S., R. Kitaura and S. Noro, 2004; Eddaoudi, M., et al., 2001; Caulder, D. L. and K. N. Raymond, 1999; Yaghi, O. M., et al., 2003). Metal-carboxylate based clusters, where metals are locked into their positions, have been synthesized in situ and successfully used as rigid directional secondary building emits to design and construct stabile open metal-organic assemblies that maintain their structural integrity even upon complete removal of their guest molecules (Li, H., M. Eddaoudi, M. O'Keeffe and O. M. Yaghi, 1999; Chui, S. S.-Y., et al., 1999; Yaghi, O. M et al., 2000; Yaghi, O. M., et al., 2003).
Although the number of topologies found in natural and synthetic inorganic zeolites, four-connected nets, is large (over 161 structures), prior attempts to construct ZMOFs from tetrahedral molecular building blocks and ditopic linkers have frequently lead to structures not related to zeolite topologies (mainly cubic diamond topology: Yaghi, O. M., et al, 2003). Zeolites, alumino-silicate networks, are purely inorganic microporous crystalline materials constructed from tetrahedral building blocks sharing corners, [SiO4]4− and [AlO4]5−. The introduction of aluminum in the silicate lattice generates a negative charge on the zeolite framework. The resulting anionic framework charge is balanced by positively charged inorganic or organic cations. These cations, accessible through the pores, provide zeolites with their large ion-exchange capacity and their utility as size- or shape-selective catalysts (Davis, M. E., 1993). Extension of their use to other applications has been hindered by several difficulties in functionalizing and widening their pores without changing their overall topology (Davis, M. E., 2002). Their structure is based on tetrahedral building blocks linked together to form different cage types or channels.
Metal organic frameworks constructed from tetrahedral building units and having zeolite-net-like topologies are scarce; however, a dominant number of inorganic zeolites are constructed from tetrahedral building units. Attempts to construct MOFs with zeolite-like topology based on the assembly of such building units have constantly lead to the formation of a cubic diamond-like topology, regarded as the default structure for the assembly of extended 3-I frameworks from 4 connected nodes. The cubic diamond-like topology (TX2) is considered the default structure for the assembly of simple tetrahedral building blocks. The cubic diamond structure is expected to form if the reaction involved simple tetrahedral building blocks, particularly single metal ions connected by flexible linkers (O'Keeffe, M., et al., 2000).
It has been shown that synthesis of open frameworks by assembly of single metal ions with di-, tri-, and poly-topic N-bound organic linkers such as 4,4′-bipyridine has produced many cationic framework structures and attempts to evacuate/exchange guests within the pores just about consistently resulted in a collapse of the host framework (Evans, O. et al., 2002). Also, the flexibility of the N-M-N angle in the tetrahedral building bock MN4 does not permit their use as a neat directional secondary building unit to design and construct complex structures other than the default cubic diamond structure.